1. Field of the Invention
The present invention relates to a magnetic lock device that makes use of the attracting action of magnetism.
2. Description of the Prior Art
A conventional magnetic lock device comprises two parts, one of which provides magnetically attracting action and includes a permanent magnet having a center bore therethrough and having a first side for providing one polarity and a second side opposite the first side for providing the opposed polarity, a first ferromagnetic plate rigidly attached to the first side of the permanent magnet, and a nonmagnetic enclosure having a center bore aligned with the center bore of the permanent magnet for packaging the permanent magnet and enclosure into one unit, and this part may be referred to as the "magnetically attracting part". The other part is magnetically attracted by the magnetically attracting part and includes a second ferromagnetic plate to be detachably attached to the magnetically attracting part, and the other part may be referred to as the "magnetically attracted part". The first ferromagnetic plate may have a rod of ferromagnetic material extending therefrom or not, and the second ferromagnetic plate has a rod of ferromagnetic material extending therefrom which can meet the first ferromagnetic plate or its rod when the rod of the second ferromagnetic plate is inserted into the center bores through the enclosure and permanent magnet. The magnetic lock device may be used as attachments for handbags, baggage and other similar bags, or clothing, belts, and other similar articles.
The conventional magnetic lock device is constructed such that a magnetic circuit may be concluded by the permanent magnet and the first and second ferromagnetic plates when the two parts are to be coupled together. In the magnetic circuit, the magnetic lines of force from the permanent magnet may be centered onto the rods that meet each other or the rod that directly engages the corresponding ferromagnetic plate inside the bores. Thus, a powerful magnetic attraction may be provided.
The conventional magnetic lock device is based on the principle of operation in which the magnetic lines of force that emanate from one pole of the permanent magnet pass through the magnetic circuit toward the opposed pole. Specifically, those magnetic lines of force pass through the first and second ferromagnetic plates, centering onto the rod or rods through which they are directed to the point at which the rods meet or the rod directly engages the corresponding plate. This way, the magnetic flux density may be increased at that meeting point.
According to the conventional magnetic lock device, each of the first and second ferromagnetic plates is made of iron, which is usually one mm thick so as to meet reduced-size requirements. Because of its reduced thickness, the plate will tend to reach its saturation point of magnetization prematurely, above which point no more magnetic lines of force can be transmitted to its rod. Those magnetic lines of force will be lost as external magnetic leaks. A more powerful permanent magnet may be used to compensate for the loss, but the magnetic attraction cannot be increased because the magnetization is saturated prematurely.